ホオジロガモ 対 カオジロオタテガモ

The most reliable field mark to separate Common Goldeneye from White-headed Duck is the head and bill pattern in adults: male Common Goldeneye shows a dark, iridescent green head with a round white spot below the eye and a normal duck bill, while male White-headed Duck has a striking white head with a black crown and a swollen, bright blue bill. Females of both species are duller, but female Common Goldeneye has a brown head and yellowish bill, contrasting with the White-headed Duck female's white face and dark cheek stripe. In flight or at a distance, Goldeneye is larger and more compact, with a less spiky tail and a more typical duck silhouette, while White-headed Duck often appears small, round-bodied, and short-necked, with a stiff, spiky tail. Juvenile and immature plumages are less distinctive, but the overall structure and head/bill shape remain useful. Both species are diving ducks, but White-headed Duck is much more likely to swim away than to take flight.

1. Adult male head pattern: Male Common Goldeneye has a dark, iridescent greenish-black head with a round white spot below the eye; male White-headed Duck has a mostly white head with a black crown and nape. This is the single most reliable mark in adult males.
2. Bill color and shape (males): Male Goldeneye has a normal, dark duck bill; male White-headed Duck has a swollen, bright blue bill, which is unique and diagnostic at close range.
3. Female head and face: Female Goldeneye has a uniform brown head and yellowish bill, while female White-headed Duck shows a white face with a dark cheek stripe and cap, and a dark bill. Use the face pattern for separation in dull-plumaged birds.
4. Body shape and size: Goldeneye is larger, longer, and more robust, with a typical duck silhouette; White-headed Duck is smaller, rounder, and more compact, with a short neck and a stiff, often upturned tail. This is useful at a distance or in flight.
5. Tail shape: White-headed Duck often holds its tail stiffly upright, especially when swimming or resting; Goldeneye has a normal, rounded duck tail.
6. Flight behavior: Goldeneye is more likely to flush and fly when disturbed; White-headed Duck prefers to dive or swim away, rarely taking flight unless pressed.
7. Plumage (body): Male Goldeneye has a white neck and belly with a dark back; male White-headed Duck has a reddish-grey body. Females are both dull but differ in head pattern as above.
8. Bill color (females): Female Goldeneye has a yellowish bill, while female White-headed Duck has a dark bill. This can be subtle but is useful at close range.
9. Habitat context: If seen in northern or boreal regions, Goldeneye is much more likely; White-headed Duck is restricted to southern Europe, North Africa, and parts of Asia.
10. Eye color: Goldeneye has striking golden-yellow eyes in adults of both sexes; White-headed Duck's eye color is not described as distinctive in the notes, so use with caution.
11. No distinctive wing pattern: Neither species is described as having a unique upperwing or flight pattern for field separation, so rely on head, bill, and structure.
12. Juvenile/immature birds: Head and bill shape remain the best clues, as plumage is less distinctive in young birds.
13. Mixed flocks: If seen with other Oxyura species (e.g., Ruddy Duck), White-headed Duck may hybridize, but hybrids show intermediate features; Goldeneye does not hybridize with Oxyura.
14. Leg and foot color: Goldeneye has orange-yellow legs and feet; this is rarely visible but can help if seen well.
15. Behavior on water: White-headed Duck often sits low in the water and may cock its tail; Goldeneye sits higher and shows a more typical duck posture.

Common Goldeneye is significantly heavier (average 900g) and slightly longer (up to 51cm) than White-headed Duck (average 665g, up to 48cm). Goldeneye also has a broader wingspan (77–83cm) compared to the more compact White-headed Duck. In the field, Goldeneye appears more robust and less stubby, while White-headed Duck is noticeably smaller, rounder, and more compact, with a proportionally shorter neck and tail.

Adult male Common Goldeneye has a dark greenish-black head with a distinctive round white spot below the eye, a white neck and belly, and a dark back. Adult male White-headed Duck is unmistakable with a mostly white head, black crown and nape, and a swollen blue bill, with a reddish-grey body. Females are trickier: female Goldeneye has a brown head, grayish body, and yellowish bill, while female White-headed Duck is gray-brown with a white face, dark cheek stripe, and dark bill. Juvenile and immature plumages are not described in detail for either species in the notes, but the head pattern and bill shape remain the best clues. There are no distinctive upperwing or flight marks described for either species, so separation in flight relies on structure and head/bill contrast.

Both species are diving ducks, but White-headed Duck is especially reluctant to fly and prefers to dive or swim away from disturbance, often holding its stiff tail raised above the water. Common Goldeneye is more likely to flush and fly when approached. In flight, Goldeneye shows a typical duck flight style, while White-headed Duck's flight is less frequently observed and may seem more labored due to its short wings and compact body.

Common Goldeneye is a medium-sized sea duck, often found on larger lakes, rivers, and coastal waters, especially in winter. White-headed Duck prefers lakes with open water and dense marginal vegetation, and is more often found in southern Europe, North Africa, and Central/Western Asia. Habitat overlap is limited, but both can be found on large, vegetated lakes during migration or winter.